Adds ability to specify short switches and aliases and POC for objects as defaults.

[chuegle]

Specify what short switch an argument should receive:

@command(options={
  "b": "baz",
  "o": "foo",
})
def test(foo, bar=2, baz=3):
  pass

> my test -h
-o --foo
-B --bar
-b --baz

Specify a default object that gets instantiated:

class Foo:
  def __init__(alpha=1, beta=2):
    self.alpha = alpha
    self.beta = beta

  def commandr_args(self):
    return [('alpha', self.alpha), ('beta', self.beta)]

  @staticmethod
  def commandr_init(alpha, beta):
    return Foo(alpha, beta)

@command
def test(one, f=Foo("x", "y")):
  """
  Commandr's view:
  test:
    -o --one = the first arg to test
    -a --alpha = The first arg to Foo(); default x
    -b --beta = The second arg to Foo(); default y
  """
  print(f"{one}, {f.alpha} {f.beta}")
---
> my test -o Hello -a World -b "!"
Hello, World !